• Question: why do some objects get bigger and smaller, e.g doors windows?

    Asked by to Nat, Nate, Roberto, Sam, Sarah on 16 Jun 2014. This question was also asked by .
    • Photo: Sarah Casewell

      Sarah Casewell answered on 16 Jun 2014:

      Doors and windows get bigger and smaller as they expand when they get hot. Most things do this, but a small amount so we don’t always notice it. Metal things expand quite a lot when hot and shrink when cold. Doors which are made of wood also do the same thing, but absorb water as well, so they can swell up. This is why in the winter some doors fit ok, but then if it’s really wet they get tight in their frames. My front door does this!

    • Photo: Natasha Stephen

      Natasha Stephen answered on 18 Jun 2014:

      This can be true of lots of natural substances in nature. Glass, which is made of sand (a material known as silica dioxide or quartz), actually flows very slowly over time. If you ever visit an old house where the windows are over 100 years old, you might notice that the panes of glass in the windows are thicker at the bottom than at the top!

      Glass is known as a ductile solid, which means it can flow slowly despite not being in a liquid state. The same is true for one of the Earth’s internal layers; the mantle beneath the Earth’s crust. It is made up of lots of silicate minerals and these flow much the same way that glass does; slowly after long periods of time!.

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